- The Arbor actionum ('Tree of Actions'), traditionally attributed to Joannes Bassianus (c. 1150-c. 1200), was a pedagogical diagram used in medieval legal education to classify and visualize Roman civil actions (actiones). Structured like a branching tree, it organized legal remedies into categories such as in rem (real), in personam (personal), and mixed actions. It further subdivided these according to legal causes 'contract, delict, succession, and others' serving as a visual tool for law students to grasp the complexities of Justinian’s Corpus Iuris Civilis. Bassianus, a prominent jurist and teacher at the University of Bologna, played a key role in systematizing legal knowledge during the revival of Roman law in the 12th century. Ponzio da Ylerda (active c. 1270-1300), a jurist likely originating from Lleida (Spain), wrote the Summa arboris actionum, a detailed explanation and commentary on the Arbor. His work did not merely replicate the tree diagram but expanded on it, clarifying each type of action and its procedural implications. Ponzio’s Summa exemplifies the scholastic method of the time - an effort to make legal doctrine more accessible and practical. It remains a valuable source for understanding how Roman legal categories were taught and interpreted in medieval universities. This is a critical edition by Guido Rossi (1916-1986).